The disclosure relates generally to systems and methods for reducing the creation of pulsations in a fluid passing through a valve.
To form an oil or gas well, a bottom hole assembly (BHA), including a drill bit, is coupled to a length of drill pipe to form a drill string. The drill string is then positioned adjacent the earth or inserted downhole, where drilling commences. During drilling, drilling fluid, or “mud,” is circulated down through the drill string to lubricate and cool the drill bit as well as to provide a vehicle for removal of drill cuttings from the borehole. After exiting the bit, the drilling fluid returns to the surface through the annulus formed between the drill string and the surrounding borehole wall.
Instrumentation for taking various downhole measurements and communication devices are commonly mounted within the drill string. Many such instrumentation and communication devices operate by sending and receiving pressure pulses through the annular column of drilling fluid maintained in the borehole.
Mud pumps are commonly used to deliver the drilling fluid to the drill string during drilling operations. Many conventional mud pumps are reciprocating pumps, having one or more piston-cylinder assemblies driven by a crankshaft and hydraulically coupled between a suction manifold and a discharge manifold. Each piston-cylinder assembly has a piston housed within a cylinder. A suction valve positioned between the cylinder and the suction manifold is operable to control the flow of drilling fluid from the suction manifold into the cylinder. Likewise, a discharge valve positioned between the cylinder and the discharge manifold is operable to control the flow of drilling fluid from the cylinder to the discharge manifold.
During operation of the mud pump, the piston is driven to reciprocate within the cylinder. As the piston moves to expand the volume within the cylinder, the discharge valve is closed, and drilling fluid is drawn from the suction manifold through the suction valve into the cylinder. After the piston reverses direction, the volume within the cylinder decreases, the pressure of drilling fluid contained with the cylinder increases, the suction valve closes, and the now-pressurized drilling fluid is exhausted from the cylinder through the discharge valve into the discharge manifold. While the mud pump is operational, this cycle repeats, often at a high cyclic rate, and pressurized drilling fluid is continuously fed to the drill string at a substantially constant rate.
Many conventional suction and discharge valves are poppet valves, each such valve having a poppet that is movable relative to a valve seat between a seated position, wherein the poppet engages the valve seat to prevent fluid flow through the valve, and an unseated position, wherein the poppet is disengaged from the valve seat and fluid may pass through the valve. When moving between the seated and unseated positions, it is common for the poppet to shiver. As used herein, the expression “shiver” refers to the unstable movement of the poppet caused at least in part by forces exerted on the poppet from fluid passing around the poppet through the valve.
Shivering creates pulsations in the drilling fluid that may disturb the downhole communication devices and instrumentation by degrading the accuracy of measurements taken by the instrumentation and hampering communications between downhole devices and control systems at the surface. Over time, the pulsations may also cause fatigue damage to the drill string pipe and other downhole components. Moreover, when the poppet is proximate the valve seat, shivering results in repeated contact between the poppet and the valve seat. Over time, repeated impact of the poppet against the valve seat causes wear to each component that shortens their service life.